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排序方式: 共有402条查询结果,搜索用时 31 毫秒
181.
182.
Andrey I. Poddel'sky Yury A. Kurskii Alexandr V. Piskunov Nikolay V. Somov Vladimir K. Cherkasov Gleb A. Abakumov 《应用有机金属化学》2011,25(3):180-189
New triphenylantimony(V) o‐amidophenolates (AP‐Me,Et)SbPh3 (1) and (AP‐Me,iPr)SbPh3 (2) with unsymmetrically substituted N‐aryl groups and (AP‐Et,Et)SbPh3 (3) with symmetrical N‐aryl group {AP‐R1,R2 is 4,6‐di‐tert‐butyl‐N‐[2‐alkyl(R1),6‐alkyl(R2)‐phenyl]‐o‐amidophenolate dianion} were synthesized and characterized in detail. Complexes were examined for dioxygen activity. The unsymmetrical complexes 1 and 2 were found to form different geometrical isomers (A and B) of spiroendoperoxides [L‐R1,R2(O2)]SbPh3 (4 and 5, respectively) with different dispositions of peroxide group and N‐aryl fragment (methyl and peroxide group are on the same side of the molecule in the less shielded isomer A, and on different sides in the more hindered isomer B). The isomer A prevails over isomer B, reflecting the possibility of steric control on the dioxygen‐binding reaction. Complex 3, where R1 = R2 = Et, formed the isomers 6A and 6B as 50:50. The ratio 4A:4B was 60:40 (for methyl‐ethyl containing complex 4) and it increased up to 80:20 for methyl‐isopropyl‐containing 5. The molecular structure of isomers 4A and 4B was confirmed by X‐ray analysis. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
183.
184.
Oleg V. Maltsev Alexandr S. Kucherenko Alexandr L. Chimishkyan Sergei G. Zlotin 《Tetrahedron: Asymmetry》2010,21(21-22):2659-2670
Chiral ionic liquids bearing α,α-diarylprolinol units were synthesized and applied for the first time as organocatalysts for the domino reaction between α,β-enals and N-protected hydroxylamines involving aza-Michael and intramolecular acetalization steps. Corresponding 5-hydroxy-3-arylisoxazolidines with either an (S)- or (R)-configuration at C-3 were obtained in excellent yields (up to 94%) and with moderate to high enantioselectivities (64 to >99% ee). The ionic liquid supported catalyst can be easily recycled and reused for at least four times without a significant loss of chemical yield or enantioselectivity. 相似文献
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187.
Prof. Dr. Ekaterina V. Ilyakina Andrey I. Poddel'sky Alexandr V. Piskunov Georgii K. Fukin Vladimir K. Cherkasov Gleb A. Abakumov 《无机化学与普通化学杂志》2012,638(9):1323-1327
The oxidation of tin(IV) bis‐amidophenolate (APiPr)2Sn · THF ( I ) by bromine and iodine leads to the formation of monoradical mixed‐ligand complexes (APiPr)(ISQiPr)SnBr · THF ( II ) and (APiPr)(ISQiPr)SnI · THF ( III ) or diradical complexes (ISQiPr)2SnBr2 ( IV ) and (ISQiPr)2SnI2 ( V ), respectively [APiPr = dianion 4, 6‐di‐tert‐butyl‐N‐(2, 6‐diisopropylphenyl)‐o‐amidophenolate; ISQiPr = radical‐anion 4, 6‐di‐tert‐butyl‐N‐(2, 6‐diisopropylphenyl)‐o‐iminobenzosemiquinone], depending on the molar ratio of reagents (2:1 or 1:1). According to EPR data for compounds II and III , the unpaired electron is delocalized between both organic ligands. The EPR spectrum of IV in toluene matrix at 130 K is typical for diradical species with S = 1 with parameters D = 530 G, E = 105 G. The mixed‐ligand complexes II and III are unstable and undergo to symmetrization leading to formation of IV or V . The molecular structures of IV and V are determined by X‐ray analysis. 相似文献
188.
Geddes CD Parfenov A Roll D Gryczynski I Malicka J Lakowicz JR 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(8-9):1977-1983
Roughened silver electrodes are widely used for surface-enhanced Raman scattering (SERS). We tested roughened silver electrodes for metal-enhanced fluorescence. Constant current between two silver electrodes in pure water resulted in the growth of fractal-like structures on the cathode. This electrode was coated with a monolayer of human serum albumin (HSA) protein that had been labeled with a fluorescent dye, indocyanine green (ICG). The fluorescence intensity of ICG-HSA on the roughened electrode increased by approximately 50-fold relative to the unroughened electrode, which was essentially non-fluorescent and increased typically two-fold as compared to the silver anode. No fractal-like structures were observed on the anode. Lifetime measurements showed that at least part of the increased intensity was due to an increased radiative decay rate of ICG. In our opinion, the use of in situ generated roughened silver electrodes will find multifarious applications in analytical chemistry, such as in fluorescence based assays, in an analogous manner to the now widespread use of SERS. To the best of our knowledge this is the first report of roughened silver electrodes for metal-enhanced fluorescence. 相似文献
189.
For a hypergraph G and a positive integer s, let be the minimum value of l such that G is L‐colorable from every list L with for each and for all . This parameter was studied by Kratochvíl, Tuza, and Voigt for various kinds of graphs. Using randomized constructions we find the asymptotics of for balanced complete multipartite graphs and for complete k‐partite k‐uniform hypergraphs. 相似文献
190.
Michal Hušák Bohumil Kratochvíl Alexandr Jegorov Jiří Brus Jaroslav Maixner Jan Rohlíček 《Structural chemistry》2010,21(3):511-518
Simvastatin is a substance used for the treatment of hypercholesterolemia. In addition to the already known room temperature
structure of simvastatin (Čejka et al. in Acta Cryst C59:o428, 2003) two new low-temperature polymorphs were found by X-ray
powder diffraction with the phase transition at 261 and 223 K (later confirmed by DSC to be 272 and 232 K). The main differences
among three polymorphs consist in the side-chains conformation only and the phase changes are fully reversible. The structures
of the polymorphs were studied by the powder diffraction based on synchrotron radiation as well as by solid-state NMR spectroscopy. 相似文献